   (pldb/db
     [male 'John]
     [male 'Herb]
+    [male 'Mike]
     [female 'Alice]
     [female 'Jessy]
+    [female 'Nicola]
     [parent 'John 'Alice]
+    [parent 'John 'Mike]
+    [parent 'John 'Nicola]
     [parent 'Jessy 'Alice]
+    [parent 'Jessy 'Mike]
     [parent 'Alice 'Herb]
     ))
+
+(defne father [x y] ([x y] (parent x y) (male x)))
+(defne mother [x y] ([x y] (parent x y) (female x)))
 
 (defn is-grand-parent?
   "Indicates whether x is a grand-parent of y"

      (=== parents [x y]))
    ))

(defn tests []
  (pldb/with-db family-facts-db
    (println (get-ancestors 'Herb))
    (println (get-grand-parents 'Herb))
    (println (get-couples))
    ))


(defn have-child?
  "Indicates whether x and y had a child together"
  [x y]
  (fresh [z] (father x z) (mother y z)))

(defn get-couples []
  (run* [parents]
